Measuring device



April 23, 1968 c. E, DEARDORFF ETAI. 3,378,929

MEASURING DEVICE Original Filed Oct. 23, 1961 5 Sheets-Sheet 1 MEASURINGDEVICE Arran/H:

April 23, 1968 c. E. DEARDORFF ETAL. 3,378,929

MEASURING DEVICE Original Filed Oct. 23, 1961 5 Sheets-Sheet 5 223 Z227Zi? f' 24? iff fn l w N ENToRs. /55 g; gmt/mv wma/4QF;

/66 /70 www J Wan/wf United States Patent O 3,378,929 MEASURING DEVICEClinton E. Deardorff and Edward John Williams, Woodland Hills, Calif.,assignors to Primus Mfg., Inc., San Lorenzo, Puerto Rico, a corporationof California Continuation of application Ser. No. 147,012, Oct. 23,1961. This application Jan. 3, 1967, Ser. No. 622,837 8 Claims. (Cl.33-125) ABSTRACT F THE DISCLOSURE Improvements in and for afriction-wheel distance measuring device of the type described in U.S.Patent 3,311,985 are described. The improvements include a resettablecoarse-reading visual indicator mounted to a metering wheel shaft, thecoupling of the coarse-reading indicator to the shaft permitting thisindicator to be reset or zeroed while the metering wheel and measurementsurface along which the wheel rolls are engaged without causing themetering wheel to slip relative to the measurement surface. An improvedanti-backlash system for the motion amplifying gear train, viz., the useof parallel gear trains and a single anti-backlashing spring, is alsodescribed, as is an improved mounting mechanism for the housing of thedevice, The mounting mechanism includes a tongue-and-groove typeconnection between the housing and the mounting mechanism and a springbiased lug engaged with the housing itself essentially directly alongthe line of the tongue-and-groove connection so that the housing cannotmove relative to the mounting mechanism independently of the biasingmechanism but arranged so that the housing may be removed readily fromthe mounting mechanism when desired.

Cross references lo related applications This application is acontinuation of application Ser. No. 147,012 filed Oct. 23, 1961, byClinton E. Deardorlf and Edward I. Williams, The measuring device inwhich the improvements described by this invention have their principalutility is described in copending, commonlyowned application Ser. No.575,209 led Aug. 2, 1966. by Merville E. Hodge for Friction WheelMeasuring Apparatus, now issued as U.S. Patent 3,311,985, suchapplication being a continuation-in-part of application Ser. No. 359,538tiled Mar. 11, 1965, now abandoned, which application in turn was acontinuation-in-part of now abandoned application Ser. No. 153,250 filedNov. 13, 1961, as a continuation-impart of application Ser. No. 784,834tiled Dec. 16, 1958, now abandoned.

Background of the invention Field of the invention-This inventionrelates to apparatus for measuring movement along a surface such as therelative movement of a first member along the surface of a secondmember. The invention has particular reference to a measuring accessorywhich incorporates a friction drive wheel adapted to be engaged inrolling contact with the surface along which measurements are to bemade.

Environment of the invention and prior art The accessory of theinvention is intended `primarily for use on machine tools where, inresponse to relative travel between rst and second guiding members ofthe machine tool, the apparatus provides, for example, a measurement ofthe relative travel between the cutting member of the machine tool andthe work being machined. Examples of such machines are engine lathes,milling machine, shaving machines, drill presses, etc.

Practically all machine tools include a pair of guiding members, one ofwhich moves relative to the other to produce relative travel between thecutting member and the work. For example, such a pair of guiding membersmay be the carriage and bed of a planing machine. Another such pair ofguiding members may be the carriage and the cross-feed on the carriageof an engine lathe These guiding members usually have one or more flatmachine surfaces extending along the direction in which they moverelative to one another.

Prior to this invention, resort was had to micrometers and rod-actuatedindicators of limited range precision measurements. Expensivesemi-permanent installations for extended range precision measurementsare required with such devices. For example, in the case withmicrometers, stops are normally positioned between the moving surfacesof the machine. An internal or external micrometer is used to accuratelymeasure the distance between these stops in order to properly positionthe work piece relative to the cutting head, Plonger-rod actuated dialindicators may be used where only a very small amount of travel occurs.The limitation with such methods of measuring relative travel betweenelements of a machine tool is that time-consuming and usuallydimensionally unstable mounting sare required to properly utilize suchlimited range indicators.

Because of the limitations inherent in the use of micrometers and dialindicators, there has long existed a need for a compact measuringinstrument capable of providing an accurate direct reading to withinonethousandth of an inch. This instrument should have an unrestrictedrange of movement and be easy to install on existing machine tools. Itis extremely desirable, in fact in many cases mandatory, that the devicebe capable of transfer from one machine tool to another. The need forsuch versatility in use is especially prevalent in the small machineshop where capital is not available to provide such measuring devices oneach tool in the shop. For many years great expectations were held forsolving the problem by means of a friction wheel type of measuringdevice, but no such friction wheel device has ever been produced whichprovides all the requisite requirements and features. Not until theprovision of this invention has it been possible to achieve sucientaccuracy and reliability in a friction wheel measurement device.

Several opposing factors influence and affect the proper design andassembly of the apparatus required in such a friction wheel measuringinstrument. The instrument must be small in dimensions in order to beproperly mountable and usable in the great majority of applications.Directly opposed to this consideration is the fact that the smaller apart is made, the more significant becomes any error inherent in itsdimensions, particularly when it is required that the main frictionwheel of the device make one or more revolutions. Additional componentsof the apparatus, such as gears, make many more revolutions during suchtravel than does the main friction wheel. If any inaccuracies arepresent in the components, these inaccuracies are cumulative over thetotal range of travel of the device and are manifested as a total error.Devices known heretofore have not been 'able to provide an apparatuswhich eliminates or minimizes such cumulative error to`an acceptablelevel. This invention, on the other hand, by a novel combination ofelements oriented in a novel manner, provides a friction wheel devicewhich successfully meets the requirements as to size and yet which doesnot sacrifice the accuracy of the device. For example, in a six-inchtravel of the device, the total cumulative error is less thanone-thousandth of one inch. This is a standard which has heretofore notbeen achievable in any device known.

Additional factors inuencing the failure of devices known heretofore toprovide the requisite `accuracy reside in the manner of moun-ting suchdevices. In this invention, it is recognized, probably for the firsttime, that the mounting of the instrument relative to the surface :alongwhich travel is to be measured is extremely critical. If mountingtechniques and apparatus are not adequate, regardless of how accuratethe instrument itself may be, the indications provided by the instrumentwill be erroneous and unacceptable. This invention, therefore, inaddition to providing a novel combination of elements in the instrumentitself, provides a novel mounting apparatus for the device which assuresaccurate performance of the instrument. This mounting apparatus is suchas t assure proper alignment of the device with the surface to bemeasured. The mounting also provides for rapid and simple demounting ofthe instrument relative to a given surface so that the instrument may betransferred to a separate installation for use in measuring the travelrelative to a second surface. In order to so use the instrument, it isnecessary only that a plurality of mountings be provided. Each of thesemountings can be adapted to the particular problems of the machine toolto which the instrument is to be attached. Once the mountings are sopositioned, the instrument may be directly interchangeable between manymachine tools.

Summary 0f the invention Generally speaking, this invention providesimprovements in a precision machine tool accessory for accuratelymeasuring the distance the rst member of the machine tool moves withrespect to the surface of a second member of the machine tool. Theaccessory includes a rigid protective housing and a metering wheelrotatably mounted in the housing with its periphery extending outwardlyof the housing for frictional engagement with the surface of the secondmember of the machine tool. First and second indicating means aremounted to the housing and are operably connected to indicate rotationof the metering wheel. An improvement provided by the present inventioncomprises in combination, a first shaft rotatably mounted within thehousing for suporting the metering wheel in the housing and extendingexteriorly of the housing, a wheel rotation indicator mounted to theexterior end of the shaft, and resilient coupling means disposed betweenthe shaft and the wheel rotation indicator. The indicator comprises thefirst indicating means of the accessory. A second improvement providedby the present invention comprises an anti-backlash gear train meansinterconnecting the wheel and the second indicating means. Theantibacklash gear train means includes a second shaft rotatably mountedWithin the housing and connected to the second indicating means, and apair of similar gear trains connected between the shafts. One of thegears connected to the first shaft is movable angularly relative to suchshaft. Resilient means are provided for biasing the angularly movablegear, and the gear train of which such gear is a part, against the othergear train. The resiliently biasing means assure that rotation of thesecond shaft relates exactly to rotation of the first shaft asdetermined by the relation of the gears in the pair of gear trains. Inconjunction with the second indicating means, means are mounted betweensuch indicating means and its shaft for setting and resetting the secondindicating means without movement of the second shaft. Additionally, theinvention comprises improved means for mounting the accessory to theiirst machine tool member, which means includes =a member defining achannel in which an elongated straight protrusion means of the housingis slidably engageable. The mounting further includes lugged meansengageable between the channel member and the accessory land resilientmeans biasing the lugged means relative to the channel member tomaintain a lpredetermined engagement force between the wheel and thesurface of the second machine tool member, the channel member beingmounted adjacent the second machine tOol part.

Brief description of the drawing The above-mentioned and other featuresand objects of this invention will be more completely understood byreference to the following detailed description and explanation of theinvention talten in conjunction with the accompanying drawings, wherein:

FIG. l is a top plane view of the friction Wheel measuring accessory;

FIG. 2 is an enlarged longi-tudinal cross section of the accessory takenalong line II-II of FIG. 1;

FIG. 3 is a perspective representation of the gears, shafts, and contactsurface of a metric measuring accessory;

FIG. 4 is an end view of a mounting block for the accessory illustratingthe lower portion of the accessory housing engaged within the mountingblock; and

FIG. 5 is a crosssectional view of the mounting block as taken alongline V-V of FIG. 4.

Description of the preferred embodiments Referring to FIGS. 1 and 2, theaccessory 10 has an elongated, substantially rectangular housing 11. Thehousing 11 is defined by an upper portion 12 and a lower portion 13. Theexternal portions of the housing have substantially parallel upper 14and lower 15 faces. A pair of substantially parallel vertical side walls16 and 17 extend from a front face 19 rearwardly to a semicircular rearend portion 20. The housing 11 denes an internal cavity 22 within whichis enclosed la portion of the apparatus of the accessory. An opening 23is provided in the front face 19 of the housing 11 and providescommunication between the internal cavity 22 and the exterior of theaccessory 1t). A back plate 25, defining a rigid guide protrusion forthe housing, is secured to the undersurface of housing 11 by screws 26threaded from the cavity 22 through the lower housing member 13 into theback plate 25. Such a manner of securing the back plate to the housing11 limits undesired removal and tampering with the structure of theaccessory 1G.

A pair of axially aligned, substantially equi-diameter apertures orholes 30 and 31 are drilled in the upper and lower housing members 12and 13, respectively. The axis of the apertures 30 and 31 is parallel tothe front face 19 of the housing 11. A second pair of coaxiallyoriented, substantially equi-diameter apertures 32 and 33 are drilledthrough the upper :and lower housing members 12 and 13 respectively, ina location spaced from the tirst pair of apertures 30 and 31. The axisof the apertures 32 and 33 is parallel to the axis of apertures 30 and31. A third pair of apertures or holes 34 and 35 are drilled through theupper 12 and lower 13 housing members, respectively; the axis of thispair of apertures is aligned with the axis of the pair of apertures 32and 33. The apertures 34 and 35 are spaced rearwardly from the secondpair of apertures. Preferably the axes of the first, second, and thirdpairs of apertures are aligned with one another in a plane perpendicularto the front face 19 of the housing 11. Further, it is preferably thatthe diameters of the first, second and third pairs of apertures becomesuccessively smaller progressing toward the rear portion 2() of housing11.

A main or primary shaft 39 is aligned in the first pair of apertures 30and 31 coaxially of the axis of these apertures. Self-centering andself-seating bearings 40 and 41, preferably of the ball type, areengaged in apertures 30 and 31, respectively, and engage a pair oftapered shoulders 42 and 43 of shaft 40. Shoulder 43 forms the lower endof shaft 39. Shaft 39 projects beyond the upper shoulder 42 in a reduceddiameter upper extension 44 projecting beyond the upper surface 14 ofthe housing 11. A flat portion or setscrew land 45 is provided in theupper extent of the reduced diameter portion 44 of shaft 39. A retainerplate 47 is engaged against the upper surface 14 and is secured to thehousing 11 by screw means 48. An internally chamfered spacer washer 49is engaged between the underside of the retainer plate 47 and thebearing 40 to securely engaged the balls of bearing against the shoulder42. Similarly, -a spa-cer Washer 50 is engaged in the lower aperture 31and is positioned relative to the bearing 41 by an adjustment andsetscrew 51 threaded into an aperture 52 of the backplate 25.

A rst or main reduction ge-ar 55 is connected to the first shaft 39internally of the housing 11. The gear 55 is secured from rotationaldisplacement relative to the shaft 39. In FIG. 2, the gear 55 is shrunkor force fitted onto the shaft 39; however, it is within the scope ofthis invention that the gear 55 may be formed integral with the shaft39. The diameter of the gear 55 is such that the teeth 56 thereof justclear the front wall of the housing because of a recess 57 provided onthe interior side thereof to accommodate gear teeth 56. It is especiallydesirable that the diameter of the first reduction gear 55 be as largeas possible in relation to the dimensions of the housing 11, The reasonsfor this dimensional relationship will be explained below.

A precision diameter contact surface 60 is disposed concentric to theshaft 39. As illustrated in FIG. 2, the contact surface 60 is formed onthe external periphery of a contact tire 61. The contact tire is shrunkor forcefitted onto the hub of gear 55. It is not required, however,that such a construction technique as illustrated be utilized for it iswithin the scope of this invention that the conta-ct surface 60 may beformed on a Wheel integral with the shaft 39. Also, contact tire 61 canbe force-fitted or shrunk onto the shaft 39 independently of the gear55.

The diameter of the contact surface 60 is such that it protrudes throughthe opening 23 in the front face 19 of housing 11. When the accessory 10is in operation, contact surface 60 makes contact on a measurementsurface 63 of a machine tool, or any other element to be measured. Bymeasurement surface is meant the surface relative to which travel of theaccessory 10 is to be measured.

An intermediate shaft 65 is rotatably mounted in the second pair ofhousing apertures 32 and 33. The axis of shaft 65 is maintained coaxialwith the predetermined axis of apertures 32 and 33. Since the manner ofmounting and bearing the shaft 65 is similar to the manner of mountingshaft 39, further detail as to shaft 65 will not be made at this point.The ends of the shaft 65 do not project beyond the upper and lowersurfaces 14 and 15, respectively, of housing 11. A first pinion orsmall-diameter gear 66 is mounted on shaft 65 and is secured fromangular displacement relative thereto. As illustrated in FIG. 2, gear66, having teeth 67 engaging the teeth 56 of gear 55, is shrunk orforce-fitted to the shaft 65. A radial shoulder or flange 68 is providedon shaft 65 to position the gear 66 axially of the shaft 65.

A second reduction gear 69 is mounted for rotation about the axis ofshaft 65. As illustrated in FIG. 2, the second reduction gear 69 isshrunk or force-fitted onto a hub 70 of the first pinion 66. Anequivalent and alternative form of the gear combination 66 and 69 wouldbe to provide an integral gear combination, or to mount the gear 69directly to shaft 65.

The gear 69 has teeth 71 which engage a second pinion 72 secured fromangular displacement relative to a secondary shaft 75. Shaft 75 ismounted so as to be axially aligned with the axis of the apertures 34and 35. The gear 72 preferably is formed integral with shaft 75. Themounting and bearing assemblies for shaft 75 are similar to those ofshafts 39 and 65 and hence the description of those similar elementsrelating to shaft 39 will suffice at this point. It should be noted,however, that shaft 75 has an elongated reduced diameter portion 76which extends to beyond the upper surface 14 of housing 11. The geartrain described and comprised of gears 55, 66, 69 and 72 provides aspeed step-up from shaft 39 to shaft 5 75 with the result that angularmotion of tire 61 is amplie-d at shaft 75.

A pair of measurement indicators 80 and 100, associated with the main 39and secondary 75 shafts, respectively, are located on the upper surface14 of housing 11. Each measurement indicator is comprised of a dialhaving a scale thereon, a scale referencer, and a scale indexer. Thescale referencer is the element of the measurement indicator againstwhich the scale is read or cornpared to determine the reading indicatedthereby. The scale indexer, on the other hand, is the means which servesto provide relative movement between the scale and the scale referencer.

The main or primary shaft measurement indicator 80 includes a cap 81having a downwardly open interior cavity 82. The cap has a peripheralradial flange 83 at its lower end. The capI 82 further has a recess 84in the underside thereof providing clearance relative to the retainerplate 47. A scale 85 is engraved, stenciled, or otherwise marked on theflange 83 of cap 81. A scale referencer mark 86 is engraved on the uppersurface 14 of the housing 11. Preferably the scale referencer 86 liesalong the longitudinal center line of the accessory 10. In the primarymeasurement indicator 80 the scale indexer is the cap 81 providingrelative motion between the scale 85 and the scale referencer 86.

A clutch mechanism is provided internally of cap 81. An internal annulargroove 88 is formed in the lower extent of the cap cavity S2. An axiallybored collar 8.9* is secured to the upper extension 44 of shaft 39 by asetscrew 90 threaded transversely thereof. The setscrew 90 engages theflat setscrew land portion 45 and is contained wholly within the collar89, i.e., the diameter of the collar 89 is such that it is less than theinternal diameter of the cap cavity S2. A washer 91 is fitted betweenthe upper end of the collar 89 and the Lipper transverse extent of thecap cavity 82. A spring retainer ring 92 is engaged within the annularrecess 8B and supports a second washer 93.

A resiliently biased wave-washer is engaged between the upper side ofthe second washer 93 and the underside of the collar 89. The Wave-washer95 has such inherent resiliency to provide a frictional bias or contactbetween the retainer ring 92 and the collar 89 and permits frictionalrotational movement between these elements. This construction allows thecap 31 to be rotated relative to the shaft 39. However, rotation of theshaft 39, because of the frictional engagement produced by wave-washer95, normally means that the cap 81 follows the rotation without lostmotion. The import of the provision of the clutch mechanism will beexplained in detail below.

A secondary measurement indicator is associated with the secondary shaft75 adjacent the rear portion 20 of the housing 11. Measurement indicator100 includes a dial 101 of generally circular nature having a scale 102imprinted around its periphery. A pointer or indicator hand 103 issecured to the upper extension '76 of shaft 75 by a pair of washers orretainers 104 and 105. In the secondary measurement indicator 100, thetip 106 of the indicator pointer 103 comprises the scale referencer,while the shaft 75 and pointer hand 103, in combination, comprise thescale indexer.

A bezel ring retainer plate 110 is secured to the upper face 14 ofhousing 11. The bezel retainer 110 has a central aperture 111 throughwhich the extension 76 of shaft 75 projects. It also has a radial flange112 peripherally thereof at its upper extent remote from the housing 11.A bezel ring 114 is engaged with the bezel retainer 110 by means of aninner peripheral ange 115 engaged with the underside of the bezel plateange 112. A wave-washer 117 is engaged against the upper surface 14 ofthe housing 11 and biases the bezel ring 114 against the bezel retainerplate 110.

The dial plate 101 is mounted to the bezel ring 114. To accommodate theupper portion of shaft 75, the dial asf/spas plate 101 has a centralaperture 119 within which a depending cylindrical portion 12@ of thelower pointer retainer 1615 cooperates. The cylindrical portion 121ieffectively journals and fixes the upper end or extension 76 of shaft 75from vibration. A transparent crystal 121 is secured to the upper limitof the bezel ring 11d to protect the dial and pointer combination fromdamage and to prevent dirt from getting into the operative portions ofthe accessory 11i.

In the apparatus described thus far, the rotary motion transformationratios, otherwise known as gear ratios, between the main shaft 39 andthe secondary shaft 75 is lzlUN. he circumference of the contact surface66 is N measuring units in length. ln a preferred embodiment of theinvention, the circumference of surface 6@ is very closely held to sixinches in length. As is illustrated particularly in FGURE l, the cap 81associated with the primary measurement indicator Sil has six majorscale divisions, each major scale division being subdivided into tenths.The scale on cap 81 thus corresponds to inches and tenths of one inch.The lzltlN, in this case 1:60, gear ratio between the main and secondaryshafts 39 and 75, respectively, provides that the pointer 1%3 of thesecondary measurement indicator 180 makes one complete revolution forevery /lhl (1,1%) revolution of shaft 39. Accordingly, the dial forscale 162 of the secondary measurement indicator 161i is subdivided intoten major divisions with each major division being further subdividedinto tenths. Therefore, travel of pointer tip 166 past each minorsubdivision of the scale corresponds to one thousandth of an inch(t).Gl) travelled by the precision tracking surface 6d along ameasurement surface 63. To accomplish these ends in the most effectivemanner, the gear ratio between the first reduction gear and the firstpinion 66 is 11N, or in this case, 1:6. The gear ratio bett een thesecond reduction gear 69 and the second pinion 72 is 1:10. Thus, forevery complete revolution of shaft 39, shaft 75 will rotate sixty times.

The apparatus illustrated and described thus far (FlGS. l and 2)corresponds to a device especially adapted for the English system. Ametric device, illustrated schematically in Fl'G. 3, is also within thescope of this invention. The metric apparatus 130 has a primary shaft139 upon which a first reduction gear 155 is secured from angulardisplacement. A contact surface 16d, forming the outer peripheralsurface of a tire 161, is secured for rotation with shaft 139. 1n FIG.3, the contact tire 161 is disposed concentrically with the shaft 139 inorder to facilitate illustration. A first intermediate shaft 165 has alirst pinion 166 secured thereto so as not to suffer angulardisplacement relative to the shaft 165. A second reduction gear 16 isalso secured to shaft 165 and, as illustrated, is a portion of the firstpinion 166. A second intermediate shaft 170 (the third shaft in housing11) has a second pinion 171 disposed concentric thereto in a manner tobe secure from angular displacement relative to shaft 1711. Asillustrated in FIG. 3, a third reduction gear 172 is fabricated as aportion of the second pinion 171 and engages a third pinion 173 securedto the secondary shaft 175, to which a pointer 103 is attached at itsupper end.

A cap 81', identical in construction to cap 31 of FIG. 2, is secured tothe upper end of the primary shaft 139. ln order to be consistent withthe usages for which the metric device 130 is intended, the scale 85fixed to the aiige 83 of c-ap 81' is in metric units correlated to thecircumference of the contact surface 16%.

In the preferred form of the metric instrument 155i, tli maiorsubdivisions of scale correspond to centimeters with the subdivisions ofthe major divisions of scale 85' signifying millimeters, i.e., there areten minor subdivisions for each major subdivision of scale 85. ideally,there are ten major subdivisions on the circumference of scale 85.

A :1 gear ratio is preferred between shafts 139 and 175. Accordingly,gear has a pitch diameter five times that of first pinion 166.Similarly, in the preferred metric instrument 131i, the second reductiongear 169 has a pitch diameter five times that of the second pinion 171.The pitch diameter of the third reduction gear 172 is four times that ofthe third pinion 173 on shaft 175. In view of these gear ratios, thepointer 183 on shaft 175 makes one hundred (10G) revolutions for everyrevolution of cap 81 associated with the first measurement indicator 88.

Referring now to FGURE 2, a backlash system 188 is provided betweenshafts 39 and 75. In the foregoing portions of this description andexplanation of the invention, it was mentioned that it is particularlydesirable to have the shafts 39, 65, and 75 free-running or easilyrotatable in their mounting and bearing apparatus. It is also desirablethat the gears 55, 66, 69, and 72 mesh easily without binding in orderthat inherent friction in the apparatus of the instrument 1t) be reducedas fares possible. Too high a friction level inherent in the strumentmeans that it is possible for the contact surface 68 to slip relative tothe measurement surface 63 and thereby produce error in the indicatedmeasurements. However, it should be realized that, in order to provide afreely running gear system, a certain amount of play or looseness isinherent in the gear mechanism. Such inherent properties of gears workdirectly against the requirements of a precision instrument.

The backlash system 186 is provided in order to assure that rotation ofshaft 75 follows exactly the rotation of shaft 39 as determined by thegear ratios present between these two shafts. As illustrated, a circularrecess 181 is provided in the upper surface of the main reduction gear55. A first backlash reduction gear 182 is rotatably mounted on shaft 39above recess 181 and is secured axially relative to shaft 39 by aretaining ring or clip 183. First backlash reduction gear 182 has apitch diameter equal to that of first reduction gear 55. The firstbacklash reduction gear 182 meshes with a first backlash pinion 185rotatably mounted to shaft 65 between a shoulder 186 and a retainer clipor ring 187. A second backlash reduction gear 188 is disposed concentricto axis of shaft 65 and is mounted for rotational movement relative toshaft 65, but is secure from axial displacement relative to the firstbacklash pinion 185. In view of the requirements for the operation ofthe device, it is most convenient if the second backlash reduction `gear188 is shrunk or press-fit to a hub 189 of first backlash pinion 185. Asecond backlash pinion 1% is mounted on shaft 75 and is secured fromaxial and angular displacement relative to shaft 75.

A spring 193 is positioned within the recess 181 of the main reductiongear 55. The spring 193 has oppositely extending lugs or extensions atopposite ends thereof engaged within suitable sockets of the mainreduction gear 55 and the first backlash reduction gear 182. The spring1113 is resiliently preloaded in its installation between lirstreduction gear 55 and first backlash reduction gear 182 such that thebacklash gear train comprised of gears 182, 185, 1&8, and 190 is loadedagainst the main gear train comprised of gears 55, 66, 69, and 72.Because of the counter-bias between these two gear trains, any rotationmanifested at shaft 39 is exactly transferred to shaft 75. It should beapparent that the pitch diameters of gear pairs 55 and 182, 66 and 185,61 and 18S, and 72 and 190 are substantially identical to preventbinding of the gear trains.

Having reference to FIGURE 3, a backlash gear train is provided in themetric embodiment 130 of the invention. A main backlash reduction gear1% is rotatably iournallecl about primary shaft 139 and is resilientlybiased relative to shaft 139 by a spring 197. Main backlash gear 196engages a first backlash pinion 198 rotatably biased relative to shaft13% by a spring 197. Main backmounted upon the first intermediate shaft165. A second backlash reduction gear 1&9 is also rotatably journalledon the i rst intermediate shaft 165, preferably in a manner So as tomove with the first backlash pinion 198. A second backlash pinion 200and a third backlash reduction gear 201 are rotatably journalled to asecond intermediate shaft 170 and preferably are connected so that theymove together. The backlash pinion 200 is engaged with the secondbacklash reduction gear 199. The third backlash reduction gear 201 isengaged with a pinion disposed along the secondary shaft 175. Thispinion gear is secured from angular displacement relative to shaft 17 5.

AS illustrated particularly in FIGURE 3, the third drive reduction gear172 and the third backlash reduction gear 201 are disposed adjacent oneanother so as to engage a common pinion 173 on shaft 175. It is withinthe scope of this invention, however, that the gears 172 and 201 may beengaged with their own pinions, each of which is secured from angulardisplacement on shaft 175.

In order to assure that foreign particles and shop sediment do notadhere to the measurement surface 63 to interfere with the operation ofthe accessory 10, a wiper 205 is fixed to the front face 19 of thehousing 11. The wiper 205 comprises a sheet of compressible wipermaterial 206 having an aperture 207 in its central portion so that itsurrounds the portion of the contact surface 60 projecting through theopening 23 in the front face 19 of housing 11 on at least three sides.The compressible wiper material S, preferably fabricated from dense feltmaterial, is glued or bonded to the front face 19.

Spring means are provided between the housing 11 and the wiper material206 to urge the ends of the wiper material outwardly from the housingagainst the measurement surface 63. As illustrated in FIGURE 1, a pairof spring clips 208 are secured within recesses 209 provided in thefront portion of the housing 11. For example, the upper housing element12 is recessed from its mating surface to its upper surface 14. Thelower housing element 13 has an upstanding or vertical pedestal 21@engageable within the recess 209. The spring element 208, preferablyformed in configuration of a substantially square geometrical shape, isengaged over the pedestal 210 before the housing portions 12 and 13 aresecured together. The spring 203 is configured such that it normallytends to bias the lateral ends of the felt strip 206 away from thehousing 11.

In the foregoing description and explanation of the accessory, it hasbeen described how a highly accurate, fine precision measuringinstrument of the friction wheel type is possible by virtue of ourunique and novel combination of apparatus which accomplishes an end notachieved by devices known heretofore. The maintenance of properalignment between the shafts of the accessory 10 or 130, as well as theinclusion of the backlash gear trains previously described, contributessignicantly to the ultimate accuracy of the instrument. However, suchprovisions are not the only considerations leading to ultimate accuracyof the device. The diameter of the tracking surface has to be quiteaccurately fabricated so that the circumference of the surface is asclose to the requisite N number of measuring units in length as ispossible. Additionally, resistance to torsional and bending loadsimposed on the housing 11 is necessary in order that the contact surface60 does not become misaligned relative to the instrument nor that theshafts become misaligned relative to their axes such that the pitchdiameters of the gears internally of the housing change to vary theultimate gear ratio between the main shaft 39 and secondary shaft 75. Itis acknowledged that the error induced by such torsional and bendingmoments may be small, but it must be remembered that any error inherentin the mechanism is cumulative with each rotation of the main shaft 39.

While the accuracy and precision of the mechanism internally of housing11 is a major consideration in the successful practice of thisinvention, there is another aspect of this invention which has notheretofore been recognized, but which, in the case of our apparatus, hasbeen recognized and solved. This problem relates to the mounting of theaccessory 10 relative to the measurement surface 63 along whichmeasurements are to be sensed by rotation of the contact surface 60thereagainst. To illustrate, if the plane of rotation of the trackingsurface 60 is inclined relative to its direction of travel, the trackingsurface will tend to move along a trigonometric component of theactually travelled distance. If the axis of the main shaft 39 isinclined approximately two degrees or so from the plane of travel of theinstrument generally, then, while the actual travel will be along thedened plane, the instrument will not sense a component equivalent to theactual distance traveled multiplied by a difference between unity andthe cosine of the angle of error (l-.99939). While it is acknowledgedthat such a trigonometric component of the actual travel `of theinstrument is small, over a cumulative distance of, say, four or fivefeet traversed by the carriage of the machine tool relative to the bed,such a factor is manifested in significant terms and leads tointolerable error. Therefore, the axis of shaft 39 must be maintainedexactly perpendicular to the plane of travel of the instrument.

In other situations, if the plane of rotation of Contact surface 60 isinclined above or below the plane normal to the measurement surface 63and parallel to the plane of travel of the instrument 10, additionalerrors will be manifested in the device. One method of overcoming suchan error would be to provide a knife edge for contact surface 60.However, the provision of a knife edge would mean that over an extendedperi-cd of use, the sharpness of the knife edge would become eroded,irregular and reduced in diameter such that the accuracy of the devicewould suffer greatly.

If a line perpendicular to and intersecting all the axes of the shafts39, 65, and remains inthe plane of travel of the instrument but isinclined relative to a normal to the measurement surface 63, then thecharacteristics of the instrument traveling in one direction relative tothe measurement surface may be different than when the instrumenttravels in the opposite direction relative to the measurement surface63.

In order to assure that the mounting or positioning of the housing 11relative to the measurement surface 63 is accordinf7 to the criteriaspecified above, the invention further includes a mounting block ormember 220. The mounting block 220 defines a longitudinal channel in itsupper portion adapted for reception of the base plate 25 of the housing11. The channel portion of mounting block 220 comprises a pair ofcoplanar surfaces 221 and 222 spaced apart from one another along thelongitudinal center line of the mounting block. Inclined surfaces 223and 224 extend upwardly and inwardly toward one another from theopposite extents of surfaces 221 and 222, respectively. The inclinedsurface 224 is provided on a deformable lug or extension 225 formedintegral with the mounting block 220. This deformable lug is defined bya cavity or recess 226 extending longitudinally of the mounting block. Athin walled section 227 connects the guide surface 224 to the mountingblock 220 and it is in this thin walled section 227 that deflectionoccurs.

The base plate 25 fixed to the underside of housing 11 comprises rigidguide protrusion means of the housing and has a pair of coplanarsurfaces 230` and 231 aligned parallel with the undersurface 15 ofhousing 11 and spaced therefrom. A pair of inwardly and upwardlyextending surfaces 232 and 233 extend from the lower surfaces 230 and231, respectively, toward the housing undersurface 15. Such aconfiguration of the housing base plate 25 defines a male dovetailmember perpendicular to the front face 19 of housing 11; the channel inthe upper portion of the mounting block 220 comprises a female dovetailmember.

The side wall 224 of the female dovetail portion is adjustable relativeto the male dovetail inserted within mounting block 220 by means ofscrews 235 having their l l heads engaged with the lug 225 but havingtheir threaded portions extending into and engaged within the body ofthe mounting block 220.

The mounting member 22%)` has a planar lower surface 238, a planar sidesurface 239, and end surfaces 240 and 241, the side, bottom, and endsurfaces being disposed at right angles to one another. Preferably thelower channel surfaces 221 and 222 are parallel to the bottom surface238. A pair of internally tapped or threaded holes 243 and 244 areprovided in the mounting block 220 perpendicular to the base surface233. Preferably the holes 223, 224 are spaced transversely of themounting member. A similar pair of internally tapped holes 245 areformed perpendicular to the side surfaces 239. These holes 243, 244, and245 permit the mounting bracket member 229 to be secured to afoundation, with the foundation disposed either against the bottom 238or side surface 239 of mounting bracket 229.

A longitudinal bore 250 is provided through the mounting member 220 andextends between the end surfaces 240 and 241. The bore 250 has a centralreduced diameter portion 251 which is internally threaded. The reduceddiameter portion 251 defines spaced-apart cylinder or sleeve recesses252 and 253. A lug 255 extends from the mounting block end surface 248adjacent the lower surface 238; a similar lug 256 is formed on themounting block along the opposite end surface 241.

The portions of the mounting block 220 described thus far aresymmetrical about a plane transversely of the mounting block through thecenter of the reduced diameter portion 251 of bore 250. It is thuspossible to side mount the mounting block to a foundation from eitherthe right or left side merely by transposing the connection of the rod260 to be described below.

A tie rod 260 has an enlarged diameter externally threaded head 261engaged within the internally threaded reduced diameter portion 251 ofbore 258. The tie rod 260 has a reduced diameter portion 262 extendingfrom the threaded head 261 to an accessory bias adjusting knob 264. Theknob has an internal recess 265 concentric to tie rod 269 which openstoward the end of the knob disposed toward the tie rod head 261. Therecess 265 preferably is of the same diameter as the cylinder cavities252 and 253. The adjusting knob 264 is secured from axial displacementrelative to the tie rod 262. Many conventional methods of securing thetie rod to the knob are possible, but in FIGURE a dowel 266 through tierod 260 is utilized.

A hollow sleeve or cylinder 27() is engaged over the reduced diameterportion 262 of the tie rod 260. The sleevehas a longitudinal internalbore 271 extending from its end adjacent knob 264. An internal annularrim 272 is provided in the bore 271 adjacent the tie rod head 261. Theexternal diameter of sleeve or cylinder 270 is less than the diameter ofthe cavities 251, 253, and 265.

A compression spring 275 is disposed coaxially of the tie rod 262internally of the sleeve bore 271 and abuts between the inner annularrim 272 of sleeve 270 and the base surface 276 of knob cavity 265. Thecompression spring is lcontinually in compression even when the tie rodhead 261 is engaged with the adjacent end of the sleeve 270.

A radial finger 280 extends laterally from the midlength of the sleeve270. The nger 280 has an end 281 which, when positioned adjacent thechannel in the upper portion of mounting block 220 (see FIGURE 5), doesnot extend beyond the upper extent of the mounting block 220. (Suchdimensional qualities provide clearance between the underside of thehousing 11 and the finger 280 when resilient biasing of the accessoryrelative to the mounting block 220 is desired.) The tinger 280 has aplanar base plate engaging surface 282 disposed toward the mountingblock 220. The plane of surface 282 is perpendicular to the axis ofsleeve 270 and tie rod 266.

The lug or finger 280 further has a cylindrical surface 283 on a reducedradial portion disposed intermediate the finger surface 282 and theadjacent end 241 of the mounting block 220. It should be mentioned thata cylinder, as the term is used here, is not necessarily circular, butrather is that surface generated by a line moving in space at all timesparallel to a fixed reference line. FIGURE 4 illustrates the preferredconfiguration of surface 283. The positioning of stop lugs 255 and 256with respect to the bore 250 is such that, as the sleeve 270 is rotatedabout the tie rod 260, the surface 283 does not clear these lugs. Thesignificance of these geometric relationships of the finger 280 willbecome more apparent -by description of the operative cooperationbetween the mounting 220 and the housing 11.

Let it be assumed that the accessory 19 is to be used to measure thetravel of an engine lathe carriage relative to the ways or bed of thelathe. A foundation for the mounting block 220 is provided on thecarriage such that the upper surface of the foundation is perpendicularto the ways and parallel to the direction of travel of the carriage. Theconstruction of the foundation for the mounting lock is not consideredin this invention since different machine tools will require differentfoundations. (Alternatively, the foundation may provide a surfaceperpendic ular to the surface dened so as to receive surface 239 ofmounting block 220.) It is considered that it is well within the scopeof the ability of a user of this invention to provide a proper andsuitable foundation. Once a foundation has been provided, the mountingblock 220 is secured to the foundation by abutting tl e base surface 238of the mounting block with the foundation. The bottom land surfaces 221and 222 of the mounting block channel should be parallel to the plane oftravel of the carriage.

The adjustment knob 264 then is rotated until, in a preferred embodimentof the invention, approximately a one-quarter (1A) inch clearance existsbetween the end surface 241 of the mounting block 229 and the baseengaging surface 282 of finger 280. In such a position the reducedradius portion cf finger 280 abuts linger or lug 256. In rotating theknob 264 without the instrument 10 engaged within the mounting block220, the knob 264, the tie rod 260, and the sleeve 270 move as a unitsuch that there is no change in the compression in spring 275 Once theclearance has been determined between the mounting block and the finger286, the finger is rotated relative to the tie rod 262 such that thefinger is stopped or positioned by lug 256. The measurement accessory1t) is then engagcd within the mounting block by interengagement of thecooperating guide elements as illustrated in FIG- URE 4.

It should Ibe noted at this point that the mounting block 220 shouldhave been pre-positioned relative to the measurement surface or waysurface 63 so that the accessory may be slid relative to the mountingblock so that the rear end of the housing base plate 25 is less thanone-quarter inch from the rear surface 241 of the mounting block. Inother words, it should be possible to slide the accessory forwardrelative to the mounting block 220 such that when the knob 264 isrotated, the finger 289 assumes the position illustrated in FIGURE 2 Insuch a situation, the surface 283 abuts against the base plate channelsurface 231 and finger 288 is perpendicular to the underside 15 ofhousing 11 and clears surface 15. Such a situation is illustrated inFIGURE 4.

The adjustment knob 264 is then rotated so that the tie rod head 261becomes increasingly engaged with the reduced diameter portion 251 ofthe mounting block bore 250. At some point during such rotation of knob264, the vertical abutment surface 282 of finger 280 will engage therear of the housing base plate 25. Further rotation of the adjustmentknob 264 forces the housing 11 to slide relative to the mounting block220 with deformation of spring 275 until the contact surface 64I of theaccessory 10 is engaged with the measurement surface 63.

In order to prevent undue friction Ibetween the male and female dovetailelements, the surface 224 of mounting block 220 is adjusted relative tosurface 223 by screws 235. Undue friction would cause spring 275 todeflect before contact surface 60 engages measurement surface 63 and theproper engagement force therebetween would be difcult to obtain.

As soon as the precision contact surface 60 abuts the measurementsurface 63, further rotation of the adjustment knob 264 causes increasedcompressive force to be induced in the spring 275. The spring constantor stiness rate of the spring 275 is such that, in conjunction with thepitch of the threads of the tie rod head 261, one complete rotation ofthe adjustment knob 264 after such contact between surfaces 60 and 63imposes the desired compressive force between the contact surface 60 andthe measurement 63. In a preferred form of this invention, such anengagement force is on the order of forty pounds. It has been found thatthis force assures accurate tracking of the contact surface 60 relativeto the measurement surface 63 without unduly loading the bearings 40 and41 of the main shaft 39. Too small a contact force would mean thatslipping of the contact surface relative to the measurement surfacemight occur and errors in the indications of the accessory might result.Also, too high a compressive force built up in the spring 275 would leadto wear and deformation within the moving parts of the accessory.

The dimensions defining the interftting dovetail elements of the baseplate 25 and the mounting block 220 are such that there is no playbetween these parts. The alignment of the channel defining the femaledovetail portion is closely perpendicular to the measurement surface 63if the mounting block 220 has been properly installed on its particularfoundation. Therefore, when the housing 11 is engaged within themounting lblock 220, proper alignment of the accessory relative tomeasurement surface 63 is achieved.

The screws 235 engaged between the mounting block lugs 225 and themounting block body provide for tine adjustment of the dimensions of thefemale dovetail such that the accessory 10 may be conveniently removedfrom the mounting block 220, and that an undue portion of thecompressive load built up in spring 275 is not wasted in frictionbetween the mounting 220 and the housing 11.

When the measuring accessory 10 provided by this invention is installedfor indication of travel relative to a measurement surface, such assurface 63, it is intended that the instrument remain continuouslyengaged with the surface except when it is intended that the instrumentbe removed for transfer to a different environment. If the accessory isutilized, say, on an engine lathe wherein many different types ofmachining operations may be carried out, it is possible to zero theinstrument when changing from one production technique to another. Asmentioned above, it is desirable if the engagement force between theprecision contact surface 60 and the measurement surface 63 ismaintained at approximately a forty pound level. Such engagement meansshaft 39 cannot rotate. To zero the instrument in such a situation, theknob 81 associated with the first shaft measurement indicator 80 ismerely rotated until the zero indication on scale 85 is aligned with theengraved scale referencer mark 86. This is possible because of theresiliently biased friction clutch apparatus contained within cap 81.

In a similar manner, the secondary measurement indicator 100 may bezeroed by rotating the bezel ring 114 relative to the secondary shaft 75because of the resiliently biased frictional engagement between thebezel ring 114 and the housing 11 provided by the wave-Washer 117. Whenthe instrument is then utilized by traversing the carriage of themachine tool relative to the base of the tool, the primary shaftmeasurement indicator 80 is cornpletely operative because the frictionalengagement between the retainer ring, the washer 93, wave-washer 95,

and collar 89 assures that the cap 81 rotates exactly with rotation ofthe primary shaft 39.

It has -been specied that a desirable feature of the accessory 10 isthat it be readily transferable from one machine tool to another sothat, particularly in small machine shops, one accessory 10 may servemany functions. Such transferability is derived from the novelcooperation between the base 25 and the mounting block 22). If theinstrument is installed on one machine tool, it may be convenientlyremoved therefrom merely by withdrawing the finger 280 of the mountingblock sleeve 270 from engagement with the housing base 25. If themounting block -has been properly adjusted, the male dovetail portion ofbase 25 may be easily withdrawn from the female dovetail of the mountingblock 220. It is preferred that a second mounting for the accessoryalready be installed on the machine tool to which the accessory is to betransferred. Therefore, where a plurality of mounting blocks 220, eachspecifically adapted to its own unique foundation, are provided in amachine shop, one instrument 10 may find extremely wide use.

From the foregoing detailed description and explanation of the inventionit may be seen that this invention provides a highly accurate andlong-lasting machine tool measurement accesso-ry of a type which has notbeen satisfactorily achieved before this invention. Many factorscontribute to the success and operability of this invention. Not theleast of such factors is the discovery and utilization of the relationbetween the engagement force, between the contact surface 60 and ameasurement surface 63, and the life of the instrument. If theengagement forces are too high, too much of an eccentric load will beexerted upon the bearings of primary shaft 39 and precision performancerequired in such an instrument will be destroyed in a relatively shorttime. However, a competing factor With the requirement to maintainaccuracy is that some force is necessary because, if a proper contactforce is not provided, then the contact surface 60 will slip and skiprelative to the measurement surface 63. This invention contains, so faras is known, the first recognition o-f this critical factor in suchfriction wheel type measuring instruments.

The foregoing detailed description and explanation of this invention hasbeen had in conjunction with specific structural configurations; thishas been largely by way of example and is not to be considered aslimiting the scope of this invention.

What is claimed is:

1. A mounting apparatus for a friction wheel measuring device, thedevice comprising a housing having a front face, the housing including arotatable precison diameter contact surface protruding beyond the frontface, means associated with the housing for indicating the rotation ofthe contact surface relative to a measurement surface adjacent which thehousing is disposed, the housing further defining a rigid elongateprotrusion means on a lower surface of the housing, the protrusion meansextending perpendicular to the front face of the housing portion beyondwhich the contact surface protrudes, the mounting apparatus comprising amounting block connectible to a member relative to which the measurementsurface moves, the mounting block defining in an upper portion thereof achannel means slidably engageable With the housing protrusion means, thechannel means being oriented perpendicular to the measurement surfacewhen the mounting block is connected to the member relative to which themeasurement surface moves, means for adjusting the slidable engagementbetween the housing protrusion means and the mounting block channelmeans, the mounting block having a threaded bore adjacent the channelmeans, an elongate ro-d having one end engaged within the threaded boreand an opposite end disposed away from the mounting block, a hollowmember axially movable relative to the rod disposed around the rod,resilient means disposed between the rod and the hollow member normallyto urge the hollow iem'ber toward the mounting block, a portion of thehol'ow member comprising a portion engageable with the housingprotrusion means when the protrusion means is engaged in the mountingblock channel portion, the rod being axially adjustable within the borefor selectively determining the force in the resilient means, which`force is transferred to the housing protrusion means to urge thehousing toward the engagement surface so that contact between thecontact surface and the measurement surface is achieved and maintained.

2. A mounting apparatus according to claim 1 including a knob secured tothe opposite end of the rod, wherein the resilient means is acompression spring disposed between the hollow member and the knob.

3. A mounting apparatus according to claim 2 wherein the bore has anenlarged diameter portion within which the hollow member is engageable.

4. A mounting apparatus according to claim 2 wherein the bore isoriented below, centrally of, and parallel to the mounting block channelportion, and wherein the bore has a central reduced diameter portiondening spaced apart enlarged diameter poltions Within one of which thehollow member is selectively engageable in conjunction with apredetermined orientation of the mounting block relative to the memberrelative to which the measurement surface moves.

5. In apparatus for indicating motion between two relatively movableparts of a machine tool and the like, one of said parts having ameasurement surface, the apparatus including a metering assembly havinga housing, a shaft rotatably mounted in the housing, and a mete-ringwheel mounted on the shaft for rotation therewith and extending beyondsaid housing to enable frictional rolling engagement with the measuringsurface, the improvement in mounting means adapted to mount the meteringassembly to the other part of the machine tool so that the portion ofthe metering wheel which extends beyond the housing engages themeasurement surfaces in frictional rolling contact and to urge the wheelinto s-aid engagement with the measuring surface so that the wheelrotates faithfully in response relative to movement between the twoparts of the tool, the mounting means comprising a male dovetail memberconnected to an exterior surface of the housing and having planar sidesurfaces converfing toward the said exterior surface of the housing, theplanes of the converging surfaces lying perpendicular to the plane ofthe housing surface beyond which the periphery of the metering wheelextends, the male dovetail member further defining a planar surfaceparallel to the plane of rotation of the metering wheel, a mountingblock for tie metering assembly engageable with the male dovetailmember, the mounting block having a female dovetail channel in an upperportion thereof, the female dovetail defining means engage-able with theplanar surface of the male dovetail portion which is parallel to theplane of rotation of the metering wheel and spaced apart converginginclined surfaces engageable with the converging surfaces of the maledovetail member, one of the mounting block inclined surfaces beingincluded on a portion of the mounting block deformable relative to theremainder of the block, means for adjusting and preselecting theydeformation of said portion relative to the remainder of the block, theblock defining an axial bore therethrough parallel to the meansengageable with the planar surface of the male dovetail which isparallel to the plane of rotation of the metering wheel, the bore havinga threaded reduced diameter portion centrally thereof defining spacedapart enlarged diameter portions of the bore adjacent each end thereof,a tie rod having an enlarged diameter end threadably engaged within thereduced diameter portion of the bore, the tie rod having a reduceddiameter portion extending from one of the enlarged diameter portions ofthe bore, a knob secured to the reduced diameter portion of the tie rodat a location remote from the tie rod enlarged end, the knob having acavity therein concentric to the tie rod and opening toward the tie rodenlarged end, a sleeve having an annular bore therein engaged concentricwith the reduced diameter tie rod portion, the external diameter of thesleeve being less than the diameter of the enlarged diameter portions ofthe mounting block bore and less than the diameter of the knob cavity, acompression spring engaged axially of the tie rod reduced diameterportion within the sleeve bore between the sleeve and the knob normallyto urge the sleeve against the tie rod enlarged end, the sleeve beingrotatable relative to the tie rod; a finger extending radially of thesleeve intermediate the ends of the sleeve, the linger defining a-planar surface lying in a plane perpendicular to the axis of the tierod, the finger having a reduced diameter portion disposed between thesaid planar surface and the tie rod enlarged end, and a lug extendingfrom the `mounting block adjacent each enlarged diameter portion of thebore, the distance of the lug from the -axis of the bore being less thanthe radial distance of the reduced diameter portion of the finger fromthe axis of the tie rod.

6. iIn a measuring accessory for a machine tool having a metering wheelrotatably mounted in a housing and extending outwardly therefrom forfrictional rolling engagement with a surface of a first part of a tool,indicating means coupled to the wheel and responsive to rotation thereoffor indicating the distance the housing moves relatively along thesurface, and a mounting assembly for securing the accessory to a secondpart of the tool, the improvement comprising, in combination, anelongated straight guide protrusion defining a male part of a dovetailconnection and connected rigidly to the housing, the guide protrusionbeing aligned parallel to a line passing through the wheel axis ofrotation and the point of farthest extension of the wheel from thehousing, a mounting block defining a female portion of a dovetailconnection in which the guide protrusion is slidably and yet releasablyengageable, the female portion of the dovetail being disposed normal tothe surface with which the metering wheel is engaged, a lug membermounted to the mounting block for reciprocal motion relative theretoparallel to the direction of slidable movement between the dovetailportions and for releasable engagement with the end of the guideprotrusion remote from the metering wheel, -resilient means biasing thelug member relative to the mounting block, and means for imposing on theresilient means a predetermined load, the lug member and the .guideprotrusion being cooperatively arranged to transfer the predeterminedload to the housing and to the metering wheel so that the metering wheelis forcefully frictionally engaged with the surface so that the wheelrotates solely .and faithfully by reason of said frictional engagementin response to relative movement of the housing along the surface andthe indicating means accurately measures said movement.

7. In a measuring accessory for a measurement tool having a meteringwheel rotatably mounted in a housing and extending outwardly therefromfor frictional rolling engagement with a surface of a first part of atool, indicating means coupled to the wheel and responsive to rotationthereof for indicating the distance the housing moves relatively alongthe surface, and the mounting assembly for sec-uring the accessory to asecond part of the tool, the improvement comprising, in combination, anelongated straight male guide connection protrusion connectedperlmanently and rigidly to the housing, the male protrusion beingaligned parallel to a line passing through the wheel vaxis of rot-ationand the point of farthest extension of the wheel from the housing, amounting block defining an elongate female connection receptacle for themale protrusion in which the male guide protrusion is slidably and yetreleasably engageable, means for mounting the mounting block to the toolsecond part so that the female connection receptacle has its elongateextent disposed norm-al to the surface with which the metering wheel isengaged, a lug member mounted to the mounting block for reciprocalmotion relative thereto parallel to the direction of slidable movementbetween the male protrusion and the female receptacle and for releasableengagement with the end of the male guide protrusion remote from themetering wheel so that the male protrusion can be slid out of the femalereceptacle relative to the mounting block past the lug member, resilientmeans biasing the l-ug member relative to the mounting block, means forimposing on the resilient means a predetermined load, the lug member andthe male vguide protrusion being cooperatively arranged to transfer thepredetermined load to the housing and to the metering wheel so that themetering wheel is forcefully frictionally engaged with 15 the surface sothat the wheel rotates solely and faithfully by reason of saidfrictional engagement in response to relative movement of the housingalong the surface and the indicating means accurately indicates saidmovement. 8. Apparatus according to claim 7 incl-uding Aadjustable meansfor biasing said predetermined load into the resilient means.

References Cited UNITED STATES PATENTS 968,884 I8/1910 Reisner 33-1721,4332'076 10/ 1922 Green 33--172 2,105,703 1/ 1938 Self 33--1252,663,598 12/ 1953 Verderber 33-141 2,881,527 4/1959 Walter et al.33-125 FOREIGN PATENTS 988,522 8/1951 France.

866,253 2/ 1953 Germany.

474,080 8/ 1952 Italy.

WILLIAM D. MARTIN, IR., Primary Examiner.

